This invention relates to a method for removing fluorinated alcohols such as fluoroalkyl alcohols used as industrial solvents from waste gases and, according to the need, recovering the fluorinated alcohols after separating from the waste gases.
Fluoroalkyl alcohols serve as good solvents for various polymers including so-called engineering plastics such as polyamides, polyesters and polyacetals. Recently a fluoroalkyl alcohol is often used as an industrial solvent in the process of coating a polymer on, for example, metal or ceramic substrates as the solvent for the polymer. After the application of the polymer solution to the substrates the solvent is dissipated by drying with a large volume of air. Since fluoroalkyl alcohols are harmful substances having a peculiar odor, it is desirable to remove the fluoroalkyl alcohol from the waste gas of the coating and drying operations before discharging the waste gas into the atmosphere. However, the concentration of the fluoroalkyl alcohol in the waste gas is usually very low, e.g. of the order of 10.sup.3 ppm, and it is difficult to clean the waste gas so as to render the gas odorless by a conventional treatment for removing or recovering organic solvents.
There is no established method for efficiently separating fluorinated alcohols from waste gases. For the treatment of waste gases containing more popular organic solvents, there are several kinds of methods such as adsorption by activated carbon, condensation by cooling, absorption in liquids and combustion. However, for the treatment of gases containing fluoroalkyl alcohols these methods have some disadvantages, respectively. In the case of adsorption by activated carbon it is necessary to alternate adsorption and desorption at short intervals because of relatively small adsorption capacity of the adsorbent. Besides, there is the need of using a large quantity of steam for the desorption, so that if the adsorbed organic solvent is soluble in water the solvent is recovered in the form of a very dilute aqueous solution. In the case of condensation by cooling, it is necessary to greatly lower the gas temperature when the concentration of a fluoroalkyl alcohol in the gas is very low, and this is unfavorable for the saving of energy. In the case of combustion there is the problem of corrosion of the furnace by the action of hydrogen fluoride formed by the combustion of fluoroalkyl alcohols.
As to absorption of organic halogen compounds into liquids, there are proposals of using a selected organic solvent as the absorbent, such as JP 50-28387 and JP 1-245838. However, these methods generally involve a problem that vapor of the organic solvent used as the absorbent is liable to intrude into the waste gas under treatment. As another problem, in the case of physical absorption of a fluoroalkyl alcohol with water or an organic solvent the absorption soon reaches saturation because only a very small amount of the fluoroalkyl alcohol can be absorbed, so that the fluoroalkyl alcohol is liable to be liberated into the atmosphere.
Fluorinated alcohols are expensive materials. In the industrial practice of the separation of a fluroinated alcohol from a waste gas it is desirable that the separated alcohol can easily be recovered for reusing it.